Transformers or any other electromagnetic apparatuses which dissipate heat during operation should be cooled by means of a coolant which absorbs the heat resulting from losses and transfers the heat to a heat sink. Such coolant may be liquid fluids, e.g. oil in case of oil transformers, or gaseous fluids, e.g. gas in case of dry-type transformers.
Known dry type transformers have generally been constructed using one of three types of techniques: conventional dry, resin encapsulated, or solid cast. The conventional dry method uses some form of vacuum impregnation with a solvent type varnish on a completed assembly including the core and the coils or individual primary and secondary coils. A known problem with these types of transformers is the removal of heat generated by power dissipation in the windings.
U.S. Pat. No. 5,656,984 A discloses a solid insulation transformer is known which has a rectangular core covered with a compressible closed-cell foam to eliminate stress during curing of the cast dielectric material surrounding the core and during operation. Heat pipes are placed between the inner coil and the core to extract heat before the temperature builds up. For safety and to eliminate the need for a separate enclosure, an outer multi-layer casing having an incorporated grounded conductive layer is provided to cover the sides of the cast body. The outer casing prevents explosion if dielectric break down and arcing occur, and reduces the danger of electric shock. There are no additional known provisions for cooling the transformer.
In EP 1787304 A1 a compact dry transformer is disclosed which includes a magnetic material core provided with a first heat sink consisting of covers having cooling fins on the outer surface thereof. The transformer also has a coil assembly provided with a second heat sink that includes enclosures having cooling fins on the outer surface thereof. The second heat sink further includes jackets with heat pipes containing a thermo fluid having low boiling point at vacuum such as water. The heat pipes consist of evaporator portions and condenser portions having cooling fins on the outer surface thereof. Due to the heat sinks, heat dissipation efficiency of the transformer is improved.
These known methods and arrangements for heat removal are either affiliated with great efforts for installment of heat pipes and the like or it is rather inefficient as to the amount of removed heat.